Stamen

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Stamens of a Hippeastrum with white filaments and prominent anthers carrying pollen Amaryllis stamens aka.jpg
Stamens of a Hippeastrum with white filaments and prominent anthers carrying pollen

The stamen (plural stamina or stamens) is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium. [1]

Contents

Morphology and terminology

A stamen typically consists of a stalk called the filament and an anther which contains microsporangia . Most commonly anthers are two-lobed and are attached to the filament either at the base or in the middle area of the anther. The sterile tissue between the lobes is called the connective, an extension of the filament containing conducting strands. It can be seen as an extension on the dorsal side of the anther. A pollen grain develops from a microspore in the microsporangium and contains the male gametophyte.

The stamens in a flower are collectively called the androecium. The androecium can consist of as few as one-half stamen (i.e. a single locule) as in Canna species or as many as 3,482 stamens which have been counted in the saguaro (Carnegiea gigantea). [2] The androecium in various species of plants forms a great variety of patterns, some of them highly complex. [3] [4] [5] [6] It generally surrounds the gynoecium and is surrounded by the perianth. A few members of the family Triuridaceae, particularly Lacandonia schismatica and Lacandonia braziliana , [7] along with a few species of Trithuria (family Hydatellaceae) are exceptional in that their gynoecia surround their androecia.

Hippeastrum flowers showing stamens above the style (with its terminal stigma) Hippeastrum-1.jpg
Hippeastrum flowers showing stamens above the style (with its terminal stigma)
Closeup of stamens and stigma of Lilium 'Stargazer' Closeup of Lilium 'Stargazer' (the 'Stargazer lily').jpg
Closeup of stamens and stigma of Lilium 'Stargazer'

Etymology

Variation in morphology

Stamens, with distal anther attached to the filament stalk, in context of floral anatomy Mature flower diagram.svg
Stamens, with distal anther attached to the filament stalk, in context of floral anatomy

Depending on the species of plant, some or all of the stamens in a flower may be attached to the petals or to the floral axis. They also may be free-standing or fused to one another in many different ways, including fusion of some but not all stamens. The filaments may be fused and the anthers free, or the filaments free and the anthers fused. Rather than there being two locules, one locule of a stamen may fail to develop, or alternatively the two locules may merge late in development to give a single locule. [13] Extreme cases of stamen fusion occur in some species of Cyclanthera in the family Cucurbitaceae and in section Cyclanthera of genus Phyllanthus (family Euphorbiaceae) where the stamens form a ring around the gynoecium, with a single locule. [14]

Cross section of a Lilium stamen, with four locules surrounded by the tapetum Antera Lilium.jpg
Cross section of a Lilium stamen, with four locules surrounded by the tapetum

Pollen production

A typical anther contains four microsporangia. The microsporangia form sacs or pockets (locules) in the anther (anther sacs or pollen sacs). The two separate locules on each side of an anther may fuse into a single locule. Each microsporangium is lined with a nutritive tissue layer called the tapetum and initially contains diploid pollen mother cells. These undergo meiosis to form haploid spores. The spores may remain attached to each other in a tetrad or separate after meiosis. Each microspore then divides mitotically to form an immature microgametophyte called a pollen grain.

The pollen is eventually released when the anther forms openings (dehisces). These may consist of longitudinal slits, pores, as in the heath family (Ericaceae), or by valves, as in the barberry family (Berberidaceae). In some plants, notably members of Orchidaceae and Asclepiadoideae, the pollen remains in masses called pollinia, which are adapted to attach to particular pollinating agents such as birds or insects. More commonly, mature pollen grains separate and are dispensed by wind or water, pollinating insects, birds or other pollination vectors.

Pollen of angiosperms must be transported to the stigma, the receptive surface of the carpel , of a compatible flower, for successful pollination to occur. After arriving, the pollen grain (an immature microgametophyte) typically completes its development. It may grow a pollen tube and undergoing mitosis to produce two sperm nuclei.

Sexual reproduction in plants

Stamen with pollinia and its anther cap. Phalaenopsis orchid. Phalaenopsis orchid-Stipe.jpg
Stamen with pollinia and its anther cap. Phalaenopsis orchid.

In the typical flower (that is, in the majority of flowering plant species) each flower has both carpels and stamens. In some species, however, the flowers are unisexual with only carpels or stamens. ( monoecious = both types of flowers found on the same plant; dioecious = the two types of flower found only on different plants). A flower with only stamens is called androecious. A flower with only carpels is called gynoecious.

A flower having only functional stamens and lacking functional carpels is called a staminate flower, or (inaccurately) male. [15] A plant with only functional carpels is called pistillate, or (inaccurately) female. [15]

An abortive or rudimentary stamen is called a staminodium or staminode , such as in Scrophularia nodosa .

The carpels and stamens of orchids are fused into a column. [16] The top part of the column is formed by the anther, which is covered by an anther cap.

Terminology

Stamen

Stamens can also be adnate (fused or joined from more than one whorl):

They can have different lengths from each other:

or respective to the rest of the flower (perianth):

They may be arranged in one of two different patterns:

They may be arranged, with respect to the petals:

Connective

Where the connective is very small, or imperceptible, the anther lobes are close together, and the connective is referred to as discrete, e.g. Euphorbia pp., Adhatoda zeylanica . Where the connective separates the anther lobes, it is called divaricate, e.g. Tilia , Justicia gendarussa . The connective may also be a long and stalk-like, crosswise on the filament, this is a distractile connective, e.g. Salvia . The connective may also bear appendages, and is called appendiculate, e.g. Nerium odorum and some other species of Apocynaceae. In Nerium, the appendages are united as a staminal corona.

Filament

A column formed from the fusion of multiple filaments is known as an androphore. Stamens can be connate (fused or joined in the same whorl) as follows:

Anther

Anther shapes are variously described by terms such as linear, rounded, sagittate, sinuous, or reniform.

The anther can be attached to the filament's connective in two ways: [18]

Related Research Articles

Column (botany)

The column, or technically the gynostemium, is a reproductive structure that can be found in several plant families: Aristolochiaceae, Orchidaceae, and Stylidiaceae.

Canellaceae Family of flowering plants

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Plant reproductive morphology Parts of plant enabling sexual reproduction

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Theca Sheath or covering

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Commelinaceae Family of flowering plants

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Dehiscence (botany) Splitting of a mature plant structure along built-in line of weakness to release contents

Dehiscence is the splitting of a mature plant structure along a built-in line of weakness to release its contents. This is common among fruits, anthers and sporangia. Sometimes this involves the complete detachment of a part; structures that open in this way are said to be dehiscent. Structures that do not open in this way are called indehiscent, and rely on other mechanisms such as decay or predation to release the contents.

Gynoecium Female organs of a flower

Gynoecium is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of pistils and is typically surrounded by the pollen-producing reproductive organs, the stamens, collectively called the androecium. The gynoecium is often referred to as the "female" portion of the flower, although rather than directly producing female gametes, the gynoecium produces megaspores, each of which develops into a female gametophyte which then produces egg cells.

Stigma (botany) Part of a flower

The stigma is the receptive tip of a carpel, or of several fused carpels, in the gynoecium of a flower.

Sabiaceae Family of flowering plants

Sabiaceae is a family of flowering plants that were placed in the order Proteales according to the APG IV system. It comprises three genera, Meliosma, Ophiocaryon and Sabia, with 66 known species, native to tropical to warm temperate regions of southern Asia and the Americas. The family has also been called Meliosmaceae Endl., 1841, nom. rej.

Calyceraceae Family of flowering plants

Calyceraceae is a plant family in the order Asterales. The natural distribution of the about sixty species belonging to this family is restricted to the southern half of South America. The species of the family resemble both the family Asteraceae and the Dipsacaceae.

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Tetrachondra is a plant genus and a member of the family Tetrachondraceae. It comprises two species of creeping succulent, perennial, aquatic or semi-aquatic herbaceous plants. Its distribution range is disjunct: one species is endemic to New Zealand while the other one is endemic to southern Patagonia and Tierra del Fuego. These plants bear essential oils.

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<i>Lacandonia</i> Genus of flowering plants

Lacandonia is a mycoheterotrophic plant that contains no chlorophyll and has the unusual characteristic of inverted positions of the male (androecium) and female (gynoecium) floral parts, something that had not been seen in any other plants, with the exceptions of Trithuria and on occasion the related Triuris brevistylis.

Connation Term in botanical morphology

Connation in plants is the developmental fusion of organs of the same type, for example, petals to one another to form a tubular corolla. This is in contrast to adnation, the fusion of dissimilar organs. Such organs are described as connate or adnate, respectively. When like organs that are usually well separated are placed next to each other, but not actually connected, they are described as connivent.

Papilionaceous flower

Papilionaceous flowers are flowers with the characteristic irregular and butterfly-like corolla found in many, though not all, plants of the species-rich Faboideae subfamily of legumes. Tournefort suggested that the term Flores papilionacei originated with Valerius Cordus, who applied it to the flowers of the bean.

Whorl (botany)

In botany, a whorl or verticil is an arrangement of leaves, sepals, petals, stamens, or carpels that radiate from a single point and surround or wrap around the stem or stalk. A leaf whorl consists of at least three elements; a pair of opposite leaves is not called a whorl.

<i>Adenodaphne</i> Genus of shrubs

Adenodaphne is a genus of shrubs and small trees endemic to New Caledonia belonging to the family Lauraceae. The genus is related to Litsea. They have 12 chromosomes.

Floral formula Notation representing flowers structure

A Floral formula is a notation for representing the structure of particular types of flowers. Such notations use numbers, letters and various symbols to convey significant information in a compact form. They may represent the floral form of a particular species, or may be generalized to characterize higher taxa, usually giving ranges of numbers of organs. Floral formulae are one of the two ways of describing flower structure developed during the 19th century, the other being floral diagrams. The format of floral formulae differs according to the tastes of particular authors and periods, yet they tend to convey the same information.

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Bibliography